Multiple depth vias in an integrated circuit

ABSTRACT

An integrated circuit with vias with different depths stopping on etch stop layers with different thicknesses. A method of simultaneously etching vias with different depths without causing etch damage to the material being contacted by the vias.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. Nonprovisional patentapplication Ser. No. 13/918,430, filed Jun. 14, 2013, and claims thepriority of U.S. provisional application Ser. No. 61/693,381, filed Aug.27, 2012 and U.S. provisional application Ser. No. 61/660,034, filedJun. 15, 2012. The following co-pending patent application is related toand hereby incorporates by reference U.S. patent application Ser. No.13/918,388 (Texas Instruments docket number TI-68922, filed Jun. 14,2013). With its mention in this section, this patent application is notadmitted to be prior art with respect to the present invention, thecontents of which are herein incorporated by reference in its entirety.

FIELD OF THE INVENTION

This invention relates to the field of integrated circuits. Moreparticularly, this invention relates to etching of vias with differentdepths.

BACKGROUND OF THE INVENTION

Metal-insulator-metal (MIM) capacitors are well known. They aretypically formed within the interconnect layers of an integrated circuitby depositing a metallic bottom plate, depositing a capacitor dielectricand then depositing, patterning and etching a metallic top plate.Typically to save cost and processing steps the top of bottom plate ofthe MIM capacitor may be formed using one of the layers of interconnect.For high precision MIM capacitors, however, the top and bottom platesare typically formed using separate metallic layers such as TaN and arenot formed using interconnect material.

In a typical process flow for integrating a precision MIM capacitor intoan integrated circuit manufacturing flow may add two to three additionalvia patterning etching steps to accommodate the difference in via depthsto underlying interconnect level, to the capacitor bottom plate, and tothe via top plate. Typically if one via pattern and etch is used to savecost, a significant yield loss occurs due to etch damage. For example,the via to the capacitor top plate is shallow compared to the to theunderlying interconnect. Significant damage to the top plate resultingin yield loss may occur during the time when the top capacitor plate viais open while the bottom plate and interconnect vias are still beingetched. Similarly damage to the capacitor bottom plate resulting inyield loss may occur during the time when the bottom capacitor plate viais open while the interconnect via is still being etched.

Embedded metal resistors formed from such material as SiCr are typicallyless than 50 nm thick. Vias to the resistor heads are typicallysignificantly shallower than the vias to the underlying interconnect.Damage to the resistor heads caused during via overetch when a singlevia pattern and etch is attempted results in yield loss. To preventyield loss, typical manufacturing flows with embedded resistors use twovia patterns and etching steps or add processing steps to form vialanding pads on the resistor heads.

SUMMARY OF THE INVENTION

The following presents a simplified summary in order to provide a basicunderstanding of one or more aspects of the invention. This summary isnot an extensive overview of the invention, and is neither intended toidentify key or critical elements of the invention, nor to delineate thescope thereof. Rather, the primary purpose of the summary is to presentsome concepts of the invention in a simplified form as a prelude to amore detailed description that is presented later.

An integrated circuit structure which enables the formation of multipledepth vias with high yield using a single via pattern and etching steps.A high yield single via pattern and etch process for simultaneouslyforming multiple depth vias.

DESCRIPTION OF THE VIEWS OF THE DRAWING

FIG. 1A through FIG. 1C are illustrations of a MIM capacitor structureformed according to embodiments.

FIGS. 2A through 2G illustrate the major steps in the fabrication of ahigh precision MIM capacitor formed according to embodiments.

FIG. 3 illustrates an integrated circuit structure formed according toembodiments.

FIG. 4A and 4B are illustrations of a resistor structure formedaccording to embodiments.

DETAILED DESCRIPTION

The present invention is described with reference to the attachedfigures, wherein like reference numerals are used throughout the figuresto designate similar or equivalent elements. The figures are not drawnto scale and they are provided merely to illustrate the invention.Several aspects of the invention are described below with reference toexample applications for illustration. It should be understood thatnumerous specific details, relationships, and methods are set forth toprovide an understanding of the invention. One skilled in the relevantart, however, will readily recognize that the invention can be practicedwithout one or more of the specific details or with other methods. Inother instances, well-known structures or operations are not shown indetail to avoid obscuring the invention. The present invention is notlimited by the illustrated ordering of acts or events, as some acts mayoccur in different orders and/or concurrently with other acts or events.Furthermore, not all illustrated acts or events are required toimplement a methodology in accordance with the present invention.

Embodiments illustrating structures and methods for simultaneouslyforming vias with different depths with high yield using a single viapatterning and single via etching step are described. Differentthicknesses of an etch stop layer are formed over underlying structuresto which the different depth vias are to make contact. By adjusting theetch stop thicknesses, the shallowest via can be opened at about thesame time as the deepest via. Opening the different depth vias at aboutthe same time avoids the damage that may occur when one via is open tothe etch during the time a deeper via is etching and may significantlyimprove yield. The need for additional via patterning and etching stepsto accommodate the different depth vias is avoided significantlyimproving cost.

FIG. 1A shows an integrated circuit structure with a high precision MIMcapacitor formed according to an embodiment. The MIM capacitor consistsof a bottom capacitor plate 108, a capacitor dielectric 112, and acapacitor top plate 114. Etch stop layer 110 of a first thickness isformed on the capacitor bottom plate 108 and an etch stop layer of asecond thickness which consists of etch stop layer 116 plus etch stoplayer 110 is formed on the capacitor top plate 114. The thickness of theetch stop layer 110 on the bottom capacitor plate 108 and the thicknessof the etch stop layer 116 on the capacitor top plate 14 may becontrolled independently. The etch rate of the etch stop layers in anoxide plasma etch is significantly slower than the etch rate of theintermetal or interlevel dielectric (ILD) layer 124. Using thisdifference in etch rates, the thickness of the etch stop layers may beadjusted so that the shallow via 120 to the top capacitor plate 114, theintermediate depth via 118 to the capacitor bottom plate 108, and thedeep via 12 to the underlying interconnect 102 all open at approximatelythe same time. This avoids damage that may occur when an open shallowvia is exposed to plasma etch for an extended time while deeper vias arestill being etched. Vias 118, 120, and 122 may then be filled with aconductive material such as copper or tungsten to connect the capacitorbottom plate 108 and the capacitor top plate 114 to an overlying layerof interconnect 126. Substrate 100 may be an integrated circuit with oneor more levels of interconnect. Interconnect 102 may be a first metalinterconnect level or may be a higher level of interconnect. Layer 104is an etch stop layer and layer 106 is an interlevel dielectric (ILD)layer underlying the capacitor.

FIG. 1B shows an integrated circuit with a precision MIM capacitor withvias partially etched according to an embodiment. Vias are typicallyetched using a two step plasma etch. The first step ILD etch istypically an oxide etch which etches the ILD layer 124 at a rate that issignificantly faster than it etches an etch stop layer 110 and 116. Thesecond step etch stop layer etch is typically a nitride etch. As shownin FIG. 1B the thickness of the etch stop layer 110 over the bottomplate 108 is adjusted so that after the first step oxide etch theremaining etch stop layer thickness 132 is about the same as the etchstop layer 104 thickness 130 over the underlying interconnect 102.Likewise the thickness of the etch stop layer 116 plus 110 over thecapacitor top plate 114 is adjusted so that the remaining etch stoplayer thickness 134 is also approximately equal to etch stop layer 104thicknesses 130 over the interconnect 102.

The additional etch stop layer thickness needed to prevent etch damageto the underlying layer depends upon the difference in via depth and maybe calculated using the equation

${AT}_{ES} = {\left( {D_{{deep}\text{-}{via}} - D_{{shallow}\text{-}{via}}} \right)\left( \frac{{ER}_{ES}}{{ER}_{IMD}} \right)}$Where AT_(ES) is the additional etch stop layer thickness 140 or 142that is needed, D_(deep-via) is the depth of the deepest via beingetched (121 in FIG. 1A) and D_(shallow-via) is the depth of a shallowervia (117 or 119 in FIG. 1) ER_(ES) is the etch rate of the etch stoplayers in the plasma ILD via etch, and ER_(ILD) is the etch rate of theILD layers 106 (ILD1) and 124 (ILD2) in the plasma ILD via etch.

The thickness of etch stop layer 110 needed over the capacitor bottomplate 108, T_(ES-BP) isT _(ES-BP) =T _(IES) +AT _(ES-BP)where AT_(ES-BP) is the additional etch stop layer thickness needed overthe capacitor bottom plate, and T_(IES) is the thickness of the etchstop layer 1004 at the bottom of the deepest via 118.

The thickness of the etch stop layer 116 needed over the capacitor topplate 114, T_(SIN-TP) isT _(ES-TP) =T _(IES) +AT _(ES-TP) −AT _(ES-BP)where AT_(ES-TP) is the additional etch stop layer thickness needed overthe capacitor top plate 114.

An illustrative example embodiment is given in FIG. 1C. In the exampleembodiment, etch stop layer 104 is about 70 nm thick, etch stop layer110 is about 91 nm thick and etch stop layer 116 is about 11 nm thick.ILD1 layer 106 is about 50 nm thick and ILD2 layer 124 is about 1450 nmthick. Capacitor bottom plate 108 is about 70 nm thick, capacitordielectric layer 112 is about 30 nm thick, and capacitor top plate 114is about 70 nm thick. Via 118 is about 1381 nm deep, via 120 is about1178 nm deep, and via 122 is about 1570 nm deep.

For illustration purposes the etch stop layers 104, 110, and 116 aresilicon nitride (SiN) with an etch rate, ER_(SIN.) of about 40 nm/minutein a plasma oxide via etch. ILD layers 106 (ILD1) and 124 (ILD2) arePETEOS layers with an etch rate of about 400 nm/minute. Using theequations to determine the etch stop layer thickness needed for the viato the capacitor bottom plate

${AT}_{{ES}\text{-}{BP}} = {{\left( {{1570\mspace{14mu}{nm}} - {1381\mspace{14mu}{nm}}} \right)\frac{40\mspace{14mu}{nm}}{400\mspace{14mu}{nm}}} = {21\mspace{14mu}{nm}}}$and T_(ES-BP) = 70  nm + 21  nm = 91  nm

Also using the equations to determine the etch stop layer thicknessneeded for the via to capacitor top plate

${AT}_{{ES}\text{-}{TP}} = {{\left( {{1570\mspace{14mu}{nm}} - {1280\mspace{14mu}{nm}}} \right)\frac{40\mspace{14mu}{nm}}{400\mspace{14mu}{nm}}} = {32\mspace{14mu}{nm}}}$and T_(ES-TP) = 70  nm + 32  nm − 91  nm = 11  nm

The time to etch via 122 through ILD layer 106 plus ILD layer 124stopping on etch stop layer 104 is given by the total ILD thickness of1450 nm+50 nm=1500 nm divided by the etch rate of 400 nm per minutewhich equals 3.75 minutes.

The time to etch an ILD thickness of 1178 nm over the capacitor topplate is 1178/400=2.95 minutes so the etching continues for3.75−2.95=0.8 minutes into the silicon nitride etch stop layer. Sincethe plasma oxide via etch etches the silicon nitride at a rate of 40 nmper minute, 40×0.8=32 nm of silicon nitride is etched leaving 102−32=70nm SiN etch stop layer remaining This is about the same thickness asetch stop layer 104 remaining over the interconnect 102.

Similarly the time to etch an ILD thickness of 1380 nm over thecapacitor bottom plate is 1289/400=3.22 minutes so the etching continuesfor 3.75−3.22=0.53 minutes into the silicon nitride. Since the plasmaoxide via etch etches the silicon nitride etch stop layer at a rate of40 nm per minute, 40×0.53=21 nm of silicon nitride is etched leaving91−21=70 nm SiN etch stop layer remaining. This is about the samethickness as etch stop layer 104 remaining over the interconnect 102.

The example embodiment above shows that when the interconnect via 122reaches etch stop layer 104 which is about 70 nm thick, the remainingnitride over capacitor bottom plate at the bottom of via 118 is alsoabout 70 nm thick as is the remaining nitride over the capacitor topplate at the bottom of via 120. The plasma etch may then be changed to aSiN plasma etch to remove the remaining nitride from the bottom of vias118, 120, and 124. Since the remaining SiN is about the same thicknessin the bottom of the different depth vias, all vias will open atapproximately the same time without damage to the underlying materialcaused by overetch.

While the embodiment is illustrated using a high precision MIMcapacitor, this technique may be used for other applications requiringvias with different depths. In addition, the example embodiment used SiNfor an etch stop layer but other etch stop layers such as SiC oraluminum oxide may be used. Other ILD materials such as low-K HDP, HARP,or polyimide may also be used.

Another example embodiment is shown in FIG. 3. This embodiment shows aMIM capacitor plus and embedded resistor 312 with resistor head pads 310and 314 formed using the capacitor bottom plate material. {Co-pendingpatent application is related and hereby incorporated by reference: U.S.patent application Ser. No. 13/918,388, filed simultaneously with thisapplication)}. Via etch stop layer 308 is also formed over the resistorhead pads 310 and 314. The embedded resistor adds one additional levelof ILD, 304 (ILD-3) so the total ILD thickness becomes the sum of ILD1302, ILD2 306 and ILD3 304.

An additional embodiment is described in FIGS. 4A and 4B. FIG. 4A showsan integrated circuit with an embedded resistor 4008. Because resistormaterial is typically thin it is difficult to stop the via etch on theresistor material without etching damage. Conventional process flows mayrequire additional deposition and patterning steps to form via landingpads on the resistor as shown in FIG. 3. In this embodiment one viapattern and via etching step may be used to simultaneously form contactto the resistor heads 416 and 418 and to the underlying interconnect 402without damage to the resistor heads caused by via overetch. In thisembodiment, the thickness of the etch stop layer 410 on top of theresistor 408 is chosen so that when the interconnect via 412 oxideplasma etch stops on etch stop layer 404, etch stop layer is partiallyetched leaving a remaining thickness 420 which is approximately equal tothe thickness 422 of the etch stop layer 404 over the interconnect 402.

The via etch may then be changed from a plasma oxide etch to a plasmanitride etch to etch through etch stop layer 404 to form contact 412 tothe underlying interconnect 402 and also to etch through the remainingetch stop layer 410 to form contacts 416 and 418 to the resistor 408heads as is shown in FIG. 4B.

An embodiment method for etching vias with different depths withoutetching damage to underlying layers is illustrated in FIGS. 2A through2G. A high precision MIM capacitor with a shallow via to the capacitortop plate, an intermediate depth via to the capacitor bottom plate and adeep via to the underlying interconnect is used to illustrate theembodiment method but any process flow that forms vias with differentdepth may also be used.

FIG. 2A shows an interconnect level 202 on an integrated circuit 200.Interconnect level may be the first layer of interconnect over theintegrated circuit or may be a higher level of interconnect. A firstetch stop layer, ES-1, 204, is formed over the interconnect 202 and afirst intermetal dielectric layer (ILD-1) 206 is formed on ES-1 204. Inan example embodiment the interconnect is copper damascene metal, ES-1is 70 nm SiN and ILD-1 is 50 nm PETEOS.

In FIG. 2B a capacitor bottom plate 210, a capacitor dielectric, 212, acapacitor top plate 214, and a second etch stop layer ES-2 is depositedon capacitor top plate layer 214. The thickness of ES-2 is calculatedusing the equation for T_(SIN-TP). A capacitor top plate photoresistpattern 218 is formed on ES-2. In an example embodiment the capacitortop 214 and bottom 210 plates are 70 nm TiN and the capacitor dielectric212 is 30 nm SiN. ES-2 is SiN with a thickness T_(ES-TP) calculated tobe 11 nm using an ILD etch rate of 400 nm/minute and an ES etch rate of40 nm/minute.

The capacitor top plate 226, ES-2 layer 228, and capacitor dielectriclayer 224 are etched in FIG. 2C and top capacitor plate photoresistpattern 218 is removed. A capacitor bottom plate etch stop layer (ES-3)222 is then deposited. The thickness T_(ES-BP) of ES-3 is calculated tobe 91 nm using the above equations with an ILD etch rate of 400nm/minute and an ES etch rate of 40 nm/minute. ES-3 also deposits overthe capacitor top plate 226 so the total etch stop thickness (222 plus228) over the capacitor top plate becomes 91 nm+11 nm=102 nm.

A capacitor bottom plate photoresist pattern 230 is formed in FIG. 2D.

FIG. 2E shows the integrated circuit after ES-3 layer 234 and thecapacitor bottom plate 232 are etched and the capacitor bottom platephotoresist pattern 230 is removed. ILD-2 layer 236 is then depositedand a via pattern 238 formed thereon. In an example embodiment, ILD-2 is1450 nm PETEOS.

The integrated circuit is shown in FIG. 2F after the ILD portion of thevia etch. The via to the underlying interconnect 240 stops on ES-1, thevia to the capacitor bottom plate 242 stops in ES-3, and the via to thecapacitor top plate 244 stops in ES-2. The remaining thicknesses of ES-2and ES-3 is approximately equal to the thickness of ES-1. In an exampleembodiment the ILD portion of the via etch is a plasma oxide etch withabout 10:1 selectivity to SiN.

As shown in FIG. 2G, the via etch is then changed from an ILD etch to aES etch and ES-1, ES-2, and ES-3 layers are etched through to formcontact to the interconnect 240, the capacitor top plate 244, and thecapacitor bottom plate 242 respectively. In an example embodiment, theES portion of the via etch is a SiN plasma etch.

While various embodiments of the present invention have been describedabove, it should be understood that they have been presented by way ofexample only and not limitation. Numerous changes to the disclosedembodiments can be made in accordance with the disclosure herein withoutdeparting from the spirit or scope of the invention. Thus, the breadthand scope of the present invention should not be limited by any of theabove described embodiments. Rather, the scope of the invention shouldbe defined in accordance with the following claims and theirequivalents.

What is claimed is:
 1. An integrated circuit, comprising: a first levelof interconnect; an first etch stop layer with a first thickness on saidfirst level of interconnect; a first ILD layer on said first etch stoplayer; a device formed on said first ILD layer; a second etch stop layerwith a second thickness approximately equal to said first thickness plusan additional thickness approximately equal to the depth of a deep viaminus the depth of a shallow via times the ratio of an etch rate of saidetch stop layer to an etch rate of said ILD in a plasma ILD via etch; asecond ILD layer formed over said device; a second level of interconnectformed on said second ILD layer; a deep via through said first etch stoplayer and through said first ILD layer and through said second ILD layerconnecting said second level of interconnect to said first level ofinterconnect; and a shallow via through said second etch stop layer andthrough said second ILD layer connecting said second level ofinterconnect to said device.
 2. The integrated circuit of claim 1further comprising: an third depth via; where said device is a MIMcapacitor; where said second etch stop layer is on a bottom plate ofsaid MIM capacitor; a third etch stop layer on a top plate of said MIMcapacitor with a third thickness approximately equal to said firstthickness minus said second thickness plus a thickness approximatelyequal to the depth of said deep via minus the depth of said third depthvia times the ratio of the etch rate of the etch stop layer to the etchrate of the ILD in said plasma ILD via etch; and where said third etchstop layer is on top of a top plate of said MIM capacitor and said thirddepth via connects said second level of interconnect to said topcapacitor plate.
 3. The integrated circuit of claim 1 where said deviceis a resistor, where a first shallow via connects said second level ofinterconnect to a first head of said resistor and where a second shallowvia connects said second level of interconnect to a second head of saidresistor.